Sky Watchers Await a Rare Celestial Experience

Venus Won't Make a Similar Pass Between Sun and Earth Again for Another 105 Years

May 31, 2012

During the transit of Venus — the astronomical term for the event — the silhouette of the planet will appear as a tiny black spot moving across the disk of the sun. A Web animation shows how the event will appear to viewers in Richardson, Texas.

On June 5, sky watchers will be in for a rare treat as Venus passes directly between Earth and the sun, an astronomical alignment that won’t occur again for another 105 years.

During the transit of Venus – the astronomical term for the event – the silhouette of the planet will appear as a tiny black spot moving across the disk of the sun. It’s an event that scientists and astronomy enthusiasts worldwide will watch closely.

“Astronomical phenomena like this transit and eclipses are events that ordinary people can see, it’s not just a chosen few who have access to them,” said Dr. Mary Urquhart, a planetary scientist and head of the Department of Science and Mathematics Education at UT Dallas. “The Web makes it possible for people to participate regardless of location or local weather.”

The most recent transit of Venus took place in June 2004. The spectacle occurs in pairs that are eight years apart, but those pairs are separated by 105 or 121 years. The next transit will occur in December of 2117.

UT Dallas alumna Allison Pace (B.S. ’10, M.A. ’12) demonstrates the use of a Sunspotter telescope. The device projects the sun's image onto a viewing area , giving sky watchers a safe way to follow the transit of Venus.

Historically, scientists traveled great distances, overcoming difficult terrain, border disputes and military skirmishes to observe transits of Venus. The data they collected from multiple locations during each event helped determine the distance from the Earth to the sun and the size of the solar system, for example. Today, the transit is an opportunity for scientists to learn more about Venus – sunlight diffusing through its atmosphere provides information about its chemical composition.

In addition, a NASA Earth-orbiting telescope called Kepler takes advantage of the same transit phenomenon occurring around distant stars to detect planets orbiting those stars.

“If a planet orbiting a star happens to be in direct line of sight between the star and Earth, then Kepler will register a slight dimming of the light from that star as the planet transits in front of it,” said Dr. Marc Hairston, a research scientist at UT Dallas’s William B. Hanson Center for Space Sciences. “It’s exactly the same phenomenon that we will be observing as Venus transits across our sun – a decrease in the intensity of light as this tiny dot moves along.”

To date, the Kepler mission has identified more than 2,300 candidates that might be extrasolar planets, and 61 have been confirmed.

Tips for Viewing the Transit of Venus

View the transit through glasses specifically made for viewing solar events and eclipses (above), or through #14 shade welding glass. Do not use these items to look through binoculars or telescopes.

Never look directly at the sun with the naked eye or through binoculars or telescopes that aren’t equipped with the proper filters.

Choose a location with an unobstructed view of the Western horizon.

“For me, this 2012 transit is particularly special because it coincides with the discoveries from Kepler,” Urquhart said. “Kepler is using exactly the same method to discover extrasolar planets. For Kepler to detect planets in this way, the geometry has to be ideal, or we wouldn’t see a transit at all. We’re finding so many extrasolar planets, but it also means there likely are a lot more out there, because it’s a really improbable alignment.”

From North Texas, the 2012 transit of Venus will be visible from shortly after 5 p.m. June 5 until the sun sets at about 8:30 p.m. The disk of Venus appears as a tiny black spot, but unfortunately for the casual observer, its size is near the visual limit of most people’s eyes, Urquhart said.

Urquhart said projecting a magnified image of the sun onto a white surface is one of the best and safest ways to view the transit in person, but observers should follow appropriate safety precautions, including never looking at the sun with the naked eye or through binoculars or telescopes that aren’t equipped with the proper filters. The website transitofvenus.org offers safe viewing techniques as well as educational, scientific and historic information about the event.

The Texas Astronomical Society and Dallas Museum of Nature & Science are among the local organizations offering public viewing events. If the weather is uncooperative or if you can’t get outside to watch the transit, NASA will have a live webcast of the event from an observatory on Mauna Kea in Hawaii.